A lot less than you might think or be told by Mothercare or BabiesRUs! For DS1 we had a moses basket, a cot, a carseat travel system, separate stroller, bumbo seat, baby bath, play mat, bouncer chair, rocker, waaay too many clothes, a sling, a steriliser, bottles, breast pump, baby towels, changing unit, sheets, jumparoo, door bouncer, baby gym, baby sensor (to make sur baby still breathes and moves in his sleep), and a whole host of other plastic tat that never saw the light of day.
DS2 we had a cot, sling, a moses basket, a changing bag, bouncer chair, some sleep suits, a few vests and a pair of boobs. He's still here, non the worse off for not buying all the claptrap! In all honesty, all a baby really needs is somewhere safe to sleep, a method of eating be it breast or bottle, a few light bits of clothing and some blankets.